Acoustic telemetry involves acoustic devices (acoustic tags) commonly used to monitor the behavior of, e.g., marine and freshwater fish. Acoustic tags transmit a sound signal or acoustic “ping” that sends identification information and location information about a tagged animal to a receiver. The receiver converts sound signals into digital data. Post processing software processes the digital data and provides positions of the tag in up to three dimensions (3D) when at least four receivers detect the same sound signal. By determining the sound's time of arrival at the hydrophone receiver, the position of the tagged animal can be determined, allowing tracking of the host animal. Then, by tying the acoustic signature received from the transmitter to the programmed signal code, a specific animal may be identified. An array of receivers allows the movement of particular animals to be tracked.
Acoustic telemetry has been identified as a technology for observation of behavior and assessment of survival for juvenile Chinook salmon passing through the Federal Columbia River Power System. Considerable effort has been expended to understand the biological effects of implantation of acoustic tags in yearling and sub-yearling Chinook salmon. Much additional effort has gone into development of autonomous and cabled receiving systems that can be deployed at dams and elsewhere in rivers. Receiving systems detect signals emitted by the acoustic tags, process the resulting detection data to track the fish, and provide data necessary to estimate survival through dams and other routes of passage. Together, the acoustic tags and receiving systems in the Columbia River system make up the Juvenile Salmon Acoustic Telemetry System (JSATS). Although acoustic tags presently used for JSATS meet current tag burden guidelines for most yearling Chinook salmon, the tags are too large for smaller juvenile Chinook salmon, particularly those found in the lower Columbia River and estuary that enter the river downstream of Bonneville Dam. Bioeffects studies also indicate that juvenile Chinook salmon less than 95 mm in length (approximately 9 g weight) implanted with current acoustic tags have reduced survival and growth rates. Accordingly, new tag designs are needed that reduce the overall size, weight, and volume, enhance the range and lifetime, reduce adverse effects associated with implantation, and broaden the range of potential applications. The present invention addresses these needs.